1. Field of the Invention
The present invention relates to nondestructive testing of paper for mechanical properties. More particularly, the present invention relates an apparatus for testing paper ultrasonically.
2. Prior Art
Paper and paperboard strength properties are important to most converting and end-use applications. Mechanical parameters such as ultimate tensile strength, burst, and bending stiffness are the strength indicia of greatest concern to the papermaker.
Tests to ascertain these mechanical characteristics of a given paper web have, traditionally, been destructive of the test sample or specimen. Loss of the sample is of no consequence but the quantity of specialized test equipment, skills and time required to perform the full battery of such tests is enormous when it is considered that a reliable test average requires a large number of test samples.
Over the past decade, nondestructive ultrasonic methods have been developed to measure many of the mechanical properties previously measured by destructive tests. By these methods, an ultrasonic wave train is transmitted through a sample sheet and the resultant wave velocity is measured. Four independent velocity measurements are taken relative to the test sample fiber orientation and used to calculate the in-plane elastic parameters of the sheet.
Development of this ultrasonic test method has followed two basic avenues. First, "breadboard" type of instrumentation has been assembled for accumulating proof of concept data. Second, instruments are being developed to exploit the concept for continuous data acquisition on a production papermachine.
Apparently overlooked in the ultrasonic test method development are instruments that are specially suited to the needs of a quasi production laboratory where numerous test samples are required to analyze pulp refining or chemical treatment changes. Such test samples are obtained from small, laboratory scale papermachines or as hand sheets formed manually, although rapidly, from an experimental pulp. Continuous production instruments are irrelevant as there is no continuous source of the test subject.
Although a "breadboard" instrument is capable of more data per unit of time than destructive testing, approximately one hour per sample remains as a considerable time investment for the 100 to 200 samples required of a raw stock experiment.
It is therefore, an object of the present invention to provide an automated ultrasonic paper testing machine capable of determining the four in-plane elastic constants of a given sample with a total sample process time of less than fifteen minutes.